When I moved to the USA 25 years ago with an Australian ATPL I went to a FSDO and got issued with a US CPL which was endorsed with language which basically said it could not be used hire and reward. It was basically a license to train. I then went to a training organization that offered a structured ATP course and did that. Trained on a Seminole and did a flight test and got the US ATP. Bear in mind that in the USA you will not get everything on your Australian license carried over to the US license. I did the test in a twin so that's all that is on my US ATP, multi engine. I would have to do a ATP flight test in a single if I wanted to add Single Engine to my ATP..I can't comment on the converting to Australian bit as I already had that ticket. Did things the right way without shortcuts.